As more electronic devices operate at higher frequencies, a capacitor, an electronic component, requires a large capacitance and a superior impedance characteristic at high frequencies. Recently, in order to reduce the impedance at high frequencies, solid electrolytic capacitors have been investigated and produced that use a solid electrolyte, such as conductive polymer having a high electric conductivity. A rolled type solid electrolytic capacitor out of solid electrolytic capacitors with conductive polymer as a solid electrolyte has been produced for satisfying the requirement for a large capacitance due to the structure thereof easily having a larger capacitance than a capacitor having stacked electrode foils. The rolled type solid electrolytic capacitor has a structure including an anode foil and a cathode foil rolled while having a separator between the foils.
A conventional rolled type electrolytic capacitor includes a capacitor element that has an anode foil, a cathode foil, an anode terminal connected to the anode foil, a cathode terminal connected to the cathode foil, and a separator provided between the anode foil and the cathode foil. An oxide film is provided on a surface of the anode foil has by anodizing. The anode foil, the cathode foil, and the separator are rolled. The separator of the capacitor element retains solid electrolyte. The capacitor element is accommodated in a case such that the anode terminal and the cathode terminal are partially exposed to an outside of the case. An opening of this case is sealed with a sealing member.
The oxide film may be damaged while being rolled. The oxide film is formed on a cutting surface of the anode foil and the surface of the anode terminal. Thus, after forming the capacitor element, the second anodizing is preferably performed to restore the oxide film or to newly form an oxide film to subsequently retain the solid electrolyte.
In order to allow the separator to retain the solid electrolyte, the rolled capacitor element is impregnated with dispersion solution containing conductive polymer particles dispersed therein. In this method, the capacitor element is impregnated with conductive polymer particles formed in advance. Thus, this method reduces damage to the oxide film due to oxidant more than a method in which a solid electrolyte layer is formed by oxidation polymerization or chemical polymerization. Furthermore, this method can form a solid electrolyte layer more uniformly on the oxide film than chemical polymerization and oxidation polymerization. Thus, the oxide film can be protected and the damage to the oxide film due to heat for example can be suppressed, thus reducing a leakage current.
Conventional rolled type electrolytic capacitors are disclosed, for example, in Patent Literatures 1 and 2. These conventional rolled type electrolytic capacitors still may cause a large leakage current.